There is, apparently, an annoying bug in the Mint-X theme for XFCE that, in Thunar, the right-click menu for items doesn't persist; you have to hold down the button to keep the menu visible. It will work properly the first time you open Thunar

I just got an update to the mint-x-theme, and when I switched to it from Clearlooks and that annoying bug is still present in the regular Mint-X and Mint-X-Metal themes, but not in the Mint-X-Metal-XFCE theme.